<p>Al–10Si alloy, as a representative engineering aluminum alloy system, is widely used in lightweight structural components; however, further improvement in the balance between strength and ductility is still required. Gradient grain structures are considered an effective strategy for achieving strength–ductility synergy in metallic materials. Nevertheless, the influence of gradient layer depth relative to the overall thickness on mechanical response remains insufficiently understood. In this study, gradient grain structures with different depths were constructed in a 1&#xa0;mm-thick Al–10Si alloy by controlling the duration of double-sided ultrasonic shot peening (USP). Tensile results indicate that both strength and ductility are enhanced after peening, while their sensitivities to gradient layer depth differ significantly. When the gradient layer occupies approximately 50% of the thickness, most of the ductility improvement has already been achieved, whereas strength continues to increase with further deepening of the refined layer. These findings demonstrate that strength and ductility exhibit distinct structural sensitivities to gradient layer depth.</p>